Hyperalimentation therapy is the intravenous feeding of nutrients to patients. A typical solution would include a protein-carbohydrate mixture. It is used primarily to meet the patient's protein and caloric requirements which are unable to be satisfied by oral feeding. The protein may be in the form of free-amino acids or protein hydrolysate and the carbohydrate commonly is dextrose. In addition to the protein and carbohydrate, vitamins (water-soluble and fat-soluble) and electrolytes also can be supplied in this therapy.
Each of these parenteral ingredients and the combination thereof are particularly susceptible to the growth of deleterious organisms and it is desirable that they be administered to the patient in a sterile condition. In addition, the solutions are tailor made to specific patient requirements under the direction of a physician. Thus, because these protein and carbohydrate solutions must be combined close to their time of use, their compounding must be performed under sterile conditions to avoid organism growth.
As a part of this compounding, the solutions that are to be administered intravenously are transferred into a total parental nutrition bag (commonly referred to as a TPN bag). Such bags are designed for home use or use in a hospital or care facility. Once filled they can be stored for a limited period of time in a standard refrigerator. The bags are filled with the solutions by a pharmacist either by gravity or by a device known as a high speed bulk compounder. Such compounders typically are capable of supplying solutions from up to nine different source bags or containers to a receiving product bag at relatively high flow rates.
The source containers may be hung from a framework of the compounder while the receiving bag is hung from a load cell that measures the weight of the receiving bag. A pump set consisting of a number of pump legs (for example, nine or more such legs) or flow paths is designed to be used with the compounder. Each of the pump legs includes flexible tubing and terminates on one end with a piercing administration spike or similar connector that is used to connect the leg of the pump set to one of the source containers. The other end of each leg is coupled to one of the inlet ports of a common manifold equipped with an exit port that is adapted to be coupled to a fill tubing connected to the receiving TPN product bag.
In those instances where a high-speed compounder is used, each leg of the pump set is associated with a different peristaltic pump or pump station of the compounder. A microprocessor in the compounder controls each of the peristaltic pumps or pump stations to thereby control the amount of solution being supplied from each source container through the particular pump leg and the manifold to the receiving product bag. The amount of solution being supplied from each source container is in part determined by information being supplied to the microprocessor of the weight being measured at selected times by the load cell from which the receiving bag is suspended. The peristaltic pumps draw solutions from each of the source containers sequentially under the control of the microprocessor and the solutions flow through the common manifold and the fill tubing into the receiving product bag.
A typical compounder would have several source bags and affiliated tubes. Typically, there are six or nine pumping stations for six or nine different source solutions. The microprocessor in the compounder is programmed to sequentially fill the product bag with each ingredient, one at a time, by sequentially activating each of the six pump stations individually so that the solutions from each source bag are transferred via the common manifold and the fill tubing to the product bag. Then, after the product bag is supplied with the required amount of fluids, the fill tubing from the product bag is sealed.
Because all tubes in such a configuration flow into a common manifold, but only one fluid at a time is pumped through the common manifold, it is possible that some fluid from a particular source bag flows back through the common manifold and into a feed tube from another source bag containing a different fluid. The fluid that does flow back into a different feed tube is not weighed as a part of the product bag and the compounder microprocessor does not recognize that fluid as a part of the overall make-up of the product bag. The problem with this is that once the product bag receives the weight of a particular ingredient, the microprocessor shuts off that respective pump and turns to the next source bag. The microprocessor begins pumping the fluid from that second source bag into the product bag but in so doing causes the backed-up and stored fluid from the first product bag in that supply tube to now flow into the manifold and ultimately into the product bag. At that point, however, the weight gain in the product bag is recognized by the compounder microprocessor as being due to the second fluid. This error leads to the situation where too much of the first fluid is present in the product bag and not enough of the second fluid is present in the bag.
A related problem arises when one of the fluids to be introduced into the product bag is a lipid solution. Lipid solutions are essentially fat emulsions and typically are placed into a separate compartment within the product bag which is isolated from the remaining mixture until immediately before (or very soon before) the solution is administered to a patient. This isolation is necessary because the lipid solution, if mixed with the other ingredients ahead of time, clouds the overall solution mixture and renders it unusable. This phenomena is known in the art as “hazing.” Because of the undesirability of mixing lipids with the other solutions prior to the time of administration, a problem has existed in the prior art where a residual amount of the lipid solution is allowed to remain in a common volume of the manifold after a lipid solution is pumped through but before the next non-lipid solution is pumped through. When the subsequent solution is pumped through, the residual lipid solution is carried into the product bag and hazing results.